1. Technical Field
The present invention relates to devices for detecting the presence of a drop in a drip chamber or similar structure in a medical infusion system. In particular, the invention relates to detection devices of the type utilizing an electrically powered light source and a corresponding photoelectric transducer.
2. Background Art
It is known in the art to use a light source, such as a light-emitting diode, coupled with a phototransducer, such as a phototransistor, to monitor a drop path such as that found in a medical infusion system. There are several known problems in designing such a detector, due to the environment in which it must operate. Typically, a drop of fluid does not cause a large change in the detection beam relative to the intensity of the beam, thus producing a signal that can be difficult to interpret. Further, a detection system must be operable in an extremely wide range of ambient light conditions, and must take into account variations from drip chamber to drip chamber and the occurrence of misting, droplet formation and other time-varying conditions. These factors may give rise to spurious signals, as well as causing light levels to potentially fall outside of the optimal operating ranges of the detection system.
A variety of approaches to this problem are reflected in the art. U.S. Pat. No. 4,321,461, issued for an invention of Walter et al., discloses a system using a pulsed infra-red radiation emitter-and-receiver pair including a phototransistor. Negative feedback is provided to stabilize the system. A pulse system in a device for detection of emboli is disclosed in U.S. Pat. No. 4,280,495, issued for an invention of Lampert. U.S. Pat. No. 4,314,484, issued for an invention of Bowman, discloses another feedback system used to stabilize a light detection device by regulating the output of the light emitter.